The present invention relates to a pressure sensor. More specifically, the present invention relates to an absolute pressure type or a shield gauge pressure type pressure sensor which is equipped with a housing storing a sensor element and a connector case, which eliminates the influence of electromagnetic noise.
Moreover, the present invention relates to an absolute pressure type or a shield gauge pressure type pressure sensor capable of lowering the influence of high-frequency electromagnetic noise greatly. DESCRIPTION OF THE RELATED ART
The present applicant has filed a patent application as Japanese Patent Application No. H10-277629 disclosing a pressure sensor for detecting the pressure of a fluid, comprising a housing made of metal having an inner space connected to a pressure detecting space and a thin rising portion at the upper end thereof, a cylindrical pressure case made of metal having a diaphragm separating the inner space into upper and lower spaces and a thin rising portion at the upper end thereof, and a connector case made of an insulating material, said pressure sensor storing both a sensor element for detecting pressure and an electric circuit in the inner space defined by stacking the housing, the pressure case and the connector case and integrating the same by caulking each rising portion, wherein a perforating condenser is provided to the pressure case.
As a result of the study on the influence of the electromagnetic noise to the output voltage using the pressure sensor mentioned above, it had been discovered that, as is indicated in FIG. 6, the output is varied due to injection noise in the range below 10 MHz, and in the range of 10 MHz to 100 MHz. That is, when an electromagnetic noise of 10 MHz or lower is supplied, the output voltage varied in the range of xe2x88x926% to +4%, and when an electromagnetic noise in the range of 10 MHz to 100 MHz is supplied, the output voltage varied in the range of xe2x88x923% to +5%.
The present invention aims at reducing the change of output voltage due to electromagnetic noise, in an absolute pressure type or a shield gauge pressure type pressure sensor.
In order to achieve the above-mentioned aim, the pressure sensor of the present invention comprises a housing having a pressure induction hole, a sensor element comprising semiconductor elements having piezoresisting effects, a holder for fixing said sensor element, and a pressure case having an electromagnetic shield effect, wherein said sensor element, said holder and said pressure case are welded airtightly so as to define a pressure sensor body including a reference pressure space, characterized in that said pressure sensor body is retained in an electrically insulated manner within said housing.
The present invention formed the electrical insulator constituting the electrical insulation between the above-mentioned pressure sensor body and said housing as a cylindrical insulator formed of an electrical insulator inserted between the above-mentioned pressure sensor body and said housing and having at the circumference thereof a rising portion, that is, an insulator sleeve.
The present invention provided to the upper side of said pressure sensor a connector case formed of an electrical insulator and having its one end opened, the opening end portion of said connector case is extended so as to constitute said electrical insulator.
The present invention provided airtightly a perforating condenser to the above-mentioned pressure case, said perforating condenser introducing the output from the above-mentioned sensor element to a predetermined external terminal.
The present invention connected a large capacity condenser in parallel to the above-mentioned perforating condenser.